Hitherto, it is general that individual households buy foodstuff and cook them to eat. Recently, however, for the intention of effecting housework simply, life style is increased in which households buy food products, which are previously cooked in a food processing room or a central kitchen of a supermarket or the like, at supermarkets or convenience stores to eat at home. In the cooked food field, developments of not only contents but also packages with various sizes or shapes have been greatly effected in order to provide best displays by changing shapes and designs of the packages.
Especially, in a deli field, unlike a conventional sales manner in which one kind of food product is sold in large quantity, food products cooked by many cooking methods are divided into small portions for more variation and sold so that consumers can choose the products as desired. Thus, for clerks of delis at supermarkets or convenience stores, it becomes a problem that cumbersome and complication required for changing devices at the time of packaging various kinds of food products in small quantity, reduction in production efficiency caused by the complicated changing, and complicated control of packaging machine parts for respective packages for various kinds of food products in small quantity.
On the other hand, it is in trend that cooked food products in which original flavors of ingredients are utilized are desired, but food products with reduced food additives soon become rotten and have short product cycles. This causes problems of need of many hands or reduction in a yield of food processing.
As a method of preserving products for a long period, gas displacement packaging is known that preserves food products under an inert gas atmosphere to increase a distance of product distribution, reduce products that have fallen out of date, and increase production efficiency. As an example of such gas displacement packaging, JP-A-9-295677 discloses a gas filling packaging method in which a gas filling packaging tray is used that includes a tray on which a substance is placed and a lid that covers the tray, the lid having a gas blow-in inlet on a top thereof and a gas outlet therearound, to cover the entire tray with a heat-shrinkable film having a gas barrier property. This method allows gas to be blown in through the gas inlet and exhausted through the outlet around the lid, thus allowing air remaining in the tray covered by the lid to be displaced by gas.
JP-A-4-189721 discloses a method in which there is provided an insulating base plate having a heating element at an edge of a hole opened in a plate, a container is placed with a flange of the container applied to the heating element, and then filled with contents, subjected to gas displacement in a vacuum chamber, and covered with a lid, and after conveyed by a conveyer, a pressing plate is lowered from above the container to perform heat bonding of the container and the lid with a die of a heated seal device.
Further, JP-A-61-103 discloses a method in which a container made of a synthetic resin sheet is filled with contents, an opening of the container is covered with a sealing film or sheet, and then the entire opening of the container is thermally pressed from an upper surface of the sealing film or sheet by a heat roll to thermally bond a periphery of the opening.
However, the method represented by JP-A-9-295677 is a method in which the gas is simply flushed into the package through the gas blow-in inlet at the top of the lid, and the air is exhausted through the gas outlet, thus a rate of displacement when the gas displaces the air in a space in the package is low, and depending on shapes of the contents, oxygen contained in the contents cannot be sometimes displaced by the displacement gas. The entire package is covered with the heat-shrinkable film having the gas barrier property, thus cutouts of the gas blow-in inlet at the top of the lid or the gas outlet tend to break the film to cause leakage of the filled gas. Besides, because of double packaging of the container and the film, the number of packaging materials are lot, causing a problem of increase in entrepreneur's bearing of cost based on the Container and Package Recycling Law.
On the other hand, the gas displacement method disclosed in JP-A-4-189721 requires the heat element corresponding to each of various containers with different sizes or designs. This requires a seal die resistant to pressure that accommodates changes in atmospheric pressure in the chamber, and such a dedicated seal die for each container is expensive to manufacture.
The method disclosed in JP-A-61-103 causes thermal deformation of the sealing film or sheet when the sealing film or sheet is thermally pressed on the opening of the container by the heat roll. When the content protrudes beyond the depth of the container, there are problems that the content is pressed by the top film, or the films overlap to each other at flange of the container to make wrinkles and cause foreign matters to be mixed into through clearances. In addition, like the above described example, this method has a problem that, for containers with different shapes, heating dies corresponding to the shapes have to be provided.
The present invention has an object to provide a method of manufacturing a gas displacement package and a sealing package that allows air in a space and a content in the package to be displaced by gas at a high rate of displacement, complies with the Container and Package Recycling Law, and facilitates changes in shapes and sizes of the package.